1. Field of the Invention
The present invention relates to a light-weight, excellent fabrication/processing property conductive member for an electric circuit, the electric circuit provided with such a conductor member and a method of fabricating them.
2. Description of the Prior Art
In recent years, electronic appliances have been used in all the industrial fields such as household electric appliances, motor vehicles, aerospace, etc. With development of demands for miniaturization, high density and personal use, the electric circuit used for an electronic appliance or an electronic unit in these fields has not been fabricated by the conventional electric wiring system, but by a printed circuit board (PC) or flexible printed board (FPC) system in which circuit patterns are made two-dimensionally using conductor such as metal on an insulating substrate.
These PCs are fabricated as follows. First, a composite plate composed of an insulating substrate and copper foil for conductor applied thereto, such as an epoxy resin composite member and phenol resin composite member, is prepared.
On such a plate, necessary circuit patterns are masked, and is subjected to etching to remove the copper foil portion other than the circuit pattern. Thus, the desired electric circuit is formed. The copper circuit portion is coated with corrosion resistance organic high-polymer, or plated with Ni, Sn, solder, Ag or Au. Incidentally, the FPC uses the insulating substrate of a plastic film having flexibility in place of the composite material of the epoxy resin or phenol resin in the PC. It is used at a bending portion or the portion where a circuit must be three-dimensionally formed.
Further, in recent years, several techniques have been proposed for directly making a circuit pattern on an insulating substrate without using a composite plate of the insulating material and a copper foil. They are a plastic plating method (JP-A (Laid-open)-1-91363), physical vapor deposition (PVD) and chemical vapor deposition (CVD) (JP-A-61-47015). But, these methods have the following defects. In the plastic plating method, electrolytic plating cannot be made for plastic which naturally has insulating property at a high film-forming speed and with a uniform film thickness and excellent intimate contact therewith. For this reason, generally, non-electrolytic plating is first made for a plastic face and thereafter the electrolytic plating is carried out. However, the ordinary non-electrolytic plating for plastic, in which the presence of catalyst is indispensable to the plastic surface, requires many complicate fabricating steps such as adsorption of the catalyst on the surface (activation processing) and making the plastic surface coarse for improving the intimate contact of the plating layer therewith (JP-A-60-67675).
The PVD and CVD methods require high cost because they are performed in a processing device with a sophisticated vacuum system. Further, since the film forming speed in these methods is lower than the above chemical plating method, they can be only applied to the circuit with a relative small current to which a large circuit resistance of the circuit body gives no trouble. Further, a technique has also been proposed in which a circuit is formed by printing, on an insulating material, a liquid or solution conductive plastic coating or paint composed of conductive material of metallic particles or flakes of e.g. Au, Ag, Cu and Ni and binder of plastic. When such a metallic conductive plastic material is used at an FPC bending portion, generally, the circuit resistance becomes unstable. Further, the paint including a conductive material of noble metal, although it is excellent in conductivity and corrosion resistance, is expensive.